All else being equal, a higher capacity battery should produce less heat per unit of work. But of course rarely is all else equal

Can you explain the physics of that, I'm curious. I'm assuming the voltage of the individuals cells is the same in a 30 kWh pack vs a 40 kWh pack (nominally 3.6V). So, more energy density is achieved by packing more individual cells in to the same amount of space.

Or are you saying that the chemistry has been fundamentally changed so that the same sized cell has a higher mAh rating, so the number of cells is roughly the same?

Oils4AsphaultOnly wrote:Is there a charge limiter with leaf 2? I miss it very much on my 2016.

No crank starter, mechanical speedometer or charging limiter.

Stop trying to spin it. They once again force us to limit charging by manually unplugging the car and counting hours, to avoid having it sit at 100%. You know, I'm going to test drive a Bolt, and if the seats are by some miracle comfortable for me, I'll get whichever car has the better lease deal, probably meaning the Bolt. I'm tired of Nissan screwing up obvious things despite our input, and essentially telling us to live with them.

All else being equal, a higher capacity battery should produce less heat per unit of work. But of course rarely is all else equal

Can you explain the physics of that, I'm curious. I'm assuming the voltage of the individuals cells is the same in a 30 kWh pack vs a 40 kWh pack (nominally 3.6V). So, more energy density is achieved by packing more individual cells in to the same amount of space.

Or are you saying that the chemistry has been fundamentally changed so that the same sized cell has a higher mAh rating, so the number of cells is roughly the same?

Current is expressed in terms of "C", where C is the amp-hours expressed as a rate in amps. A 50amp-hour battery supply 50 amps is said to be discharging at 1C. If it supplies 100 amps, then it's discharging at 2C. Charging is also expressed in terms of those rates. Heat generation is generally proportional to the C rate, and the manufacturer will specify maximum C rates, both short-term and sustained, charging and discharging, that the battery can be subjected to. This is mostly an expression of heat-generation.

A 100 amp-hour battery delivering (or charging at) 100 amps is only working at 1C as opposed to the 50 amp-hour battery at 100 amps, which is 2C. The 50 amp-hour battery is working much harder and will generate more heat, assuming equivalent chemistries, etc... For further info, look up "intercalation" in lithium-ion batteries.

All else being equal, a higher capacity battery should produce less heat per unit of work. But of course rarely is all else equal

Can you explain the physics of that, I'm curious. I'm assuming the voltage of the individuals cells is the same in a 30 kWh pack vs a 40 kWh pack (nominally 3.6V). So, more energy density is achieved by packing more individual cells in to the same amount of space.

Or are you saying that the chemistry has been fundamentally changed so that the same sized cell has a higher mAh rating, so the number of cells is roughly the same?

Current is expressed in terms of "C", where C is the amp-hours expressed as a rate in amps. A 50amp-hour battery supply 50 amps is said to be discharging at 1C. If it supplies 100 amps, then it's discharging at 2C. Charging is also expressed in terms of those rates. Heat generation is generally proportional to the C rate, and the manufacturer will specify maximum C rates, both short-term and sustained, charging and discharging, that the battery can be subjected to. This is mostly an expression of heat-generation.

A 100 amp-hour battery delivering (or charging at) 100 amps is only working at 1C as opposed to the 50 amp-hour battery at 100 amps, which is 2C. The 50 amp-hour battery is working much harder and will generate more heat, assuming equivalent chemistries, etc... For further info, look up "intercalation" in lithium-ion batteries.

The effect you are describing is noticeable to a person without instruments at high C rates, not between one and two C. At current DCFC rates the heat generation will be proportional to kWh into the battery until the SoC is over ~ 50%. The temperature increase will be less in the 40 kWh battery due to increased heat capacity, but the heat will dissipate proportional to Newton's law and the unchanged battery surface area.

Try this: take a 30 mile drive for 30 miles at 30 mph and then at 60 mph. Correct for air friction and tell us if you can find increased battery consumption per mile.

Or this: From a low SoC (say, below 30) charge 10 kWh or up to say 60% into the battery on a > 6 kW L2 or DCFC. Compare the two wall kWh used.

Last edited by SageBrush on Wed Sep 06, 2017 4:08 pm, edited 1 time in total.